1. Field of the Invention
The present invention relates to an air conditioning system, and more particularly to a system circulating a phase-changeable fluid between a heat source side machine and a plurality of user side machines all or more than half of which are disposed below the heat source side machine, by utilizing a specific gravity difference between the liquid and the gas phases of the fluid and a driving power of an auxiliary pump for cooling, so that each of the user side machines can perform cooling operation.
2. Background Art
An air conditioning system shown in FIG. 4 is known in the prior art, which utilizes a phase-changeable fluid, i.e., a fluid that can change its phase between the liquid and gas phases by gaining and losing a latent heat, so that a power for transporting the fluid is not required.
In this system, a heat source side machine 1 serving as a condenser is set at a high position of a building, and user side machines 4 are set in rooms to be air-conditioned disposed at lower levels than the heat source side machine 1. The heat source side machine 1 is connected to heat exchangers 5 of the user side machines 4 by a liquid phase pipe 6 and a gas phase pipe 7. This configuration enables the liquid that has been condensed by discharging heat in a heat exchanger 2 of the heat source side machine 1 to flow down to the heat exchanger 5 of the user side machine 4 through the liquid phase pipe 6 by its own gravity, while the gas that has been evaporated by absorbing heat from a warm air in the heat exchanger 5 of the user side machine 4 can flow in the gas phase pipe 7 to reach the heat source side machine 1 that has become in a low pressure after condensing and liquefying of the fluid. Thus, the fluid can circulate between the heat source side machine 1 and the user side machines 4 without any driving power such as an electric pump, thereby a running cost can be saved. In FIG. 4, reference numeral 8 denotes a flow control valve, and reference numeral 9 denotes a blower.
An air conditioning system having a receiver tank 10 and an electric pump 11 connected in series and inserted in the liquid phase pipe 6 as shown with a broken line in FIG. 4 is also known in the art. In such an air conditioning system, the electric pump 11 is controlled in accordance with a liquid level of the phase-changeable fluid in the liquid phase stored in the receiver tank 10, so that the phase-changeable fluid in the liquid phase can be supplied to each of the user side machines sufficiently even if some of the user side machines are set at levels equal to or higher than the level at which the heat source side machine 1 is set.
However, in the above mentioned air conditioning system, a pressure of the fluid at a start time of cooling operation is lowest in the heat source side machine, and the pressure difference between the heat source side machine and the user side machine is large at that time. Accordingly, there was a problem that the fluid was concentrated into the heat source machine and the condensed fluid in the liquid phase could not easily flow out into the liquid phase pipe, resulting in a bad starting characteristics.
In addition, when the phase-changeable fluid is transported to each of the user side machines by a pressure generated by the electric pump, the fluid that has been supercooled in the heat source machine may be heated by a driving mechanism or a transporting mechanism of the electric pump and may become a non-supercooled state. Accordingly, there was a problem that if the fluid was further heated by an outside air via the liquid phase pipe wall before reaching each of the user side machines, the fluid in the liquid phase might boil and generates bubbles disturbing the circulation of the fluid.
Especially, when using a self-cooling type pump that is inexpensive and easy to be maintained since it utilizes a liquid transported by the pump for cooling the pump without using any cooling fan, the temperature rise of the fluid becomes large.